Method of hobbing



Jan. 25, 1955 o. E. STAPLES ET AL METHOD OF' HOBBING 8 Shets-Sheet l Filed April l2, 1949 INVENTDR` wr, mi N W2/.8.4M w W a 9 A l Jan. 25, 1955 o. E. STAPLES ET A1.

METHOD OF HOBBING 8 Sheets-Sheet 3 Filed April 12, 1949 l I. n IIT u Il I IIII IIIIIIIIIIIIIIIII- Jan. 25, 1955 o. E. STAPLES ETAL 2,700,324

METHOD 0F HOBBING Filed April 12, 1949 8 Sheets-Sheet 4 n m rQ QL,...

Jan. 25, 1955 o. E. STAPLES ET AL 2,700,324

' METHOD oF HOBBING Filed April 12, 1949 8 Sheets-Sheet 5 l l l l Arran/cys INVENTORS 027s T www /7 By Anf/wwf ier/7' @M s www.

Jan; 25, 1955 o. E. STAPLES ETAL 2,700,324

METHOD OF HOBBING ffrraefveys 8 Sheets-Sheet 7 Jan. 25, 1955 o. E. STAPLES ET AL METHOD 0F HOBBING Filed April 12, 1949 Jan- 25, 1955 o. E. STAPLES ET Ax. 2,700,324

METHOD 0F HOBBING Filed April 12, 1949 8 sheets-sheet esV l INVENTORS 4 0775 E. SP4/ua? United States Patent() METHOD oF HoBBnsG Otis E. Staples, Euclid, and Anthony J. Bent, Willoughby, Ghio, assignors to The Cleveland Hobbing Machine Company, Euclid, Ohio, a corporation of Ohio Application April 12, 1949, Serial No. 86,952

3 Claims. (Cl. 90-4) The present invention relates to machine tools and more particularly to machines for and methods of hobbing gears and the like and, particularly, to hobbing machines of the axial feed type as distinguished from tangential feed type hobbing machines.

In the operation of hobbing machines of the axial feed type, it is customary to periodically advance the hob axially, that is, move the hob tangentially of the work spindle after a number of gears have been cut and a portion of the hob dulled, so as to bring an unused section of the hob into cutting position. This practice does not make full use of the hob since the portions thereof intermediate successive settings perform very little, if any, cutting; in other words, the wear, etc., is not uniformly distributed over the entire usable or effective length of the hob.

The principal object of the invention is the provision of a novel and improved method of hobbing gears and the like, which method comprises, rotating a hob and work blank in cutting relation and in timed relation producing a relative feed movement therebetween axially of the axis of rotation of the work blank, and continuously advancing the hob at a very slow rate along its axis and in a direction opposite to the direction of movement of the engaged periphery of the work piece so that, in general, the initial cut in the blank is made by a used portion of the hob and unused portions of the hob initially engage previously cut portions of the blank. y

The invention resides in certain steps of procedure and further objects and advantages will be apparent from the following description of the preferred embodiment described with reference to the accompanying drawings forming a part of this speciiication, in which similar reference characters designate corresponding parts, and in which Fig. l is a side elevational view of a hobbing machine designed to operate according to the present invention;

Fig. 2 is a front View of the hobbing machine shown in Fig. l;

Fig. 3 is a plan view of the hobbing machine shown in Fig. l;

Fig. 4 is a sectional view taken substantially along line 4 4 of Fig. 2;

Fig. 5 is a fragmentary enlarged view, partly in section, of the hobbing machine of Fig. l, showing the Work spindle and elevation mechanism for the work head, the secion being taken substantially on line 5 5 of Figs. 6 an 7;

Fig. 6 is a sectional view taken substantially on line 6 6 of Fig. 5; l

Fig. 7 is an enlarged sectional View taken substantially along line 7 7 of Fig. 6;

Fig. 8' isla sectional view taken substantially along line 8 8 of Fig. 7; and Y Fig. 9 is a diagrammatic showing of a hob cutting teeth in a gear blank according to the invention.

Although the invention is susceptible of being performed on various types of hobbing machines, it is herein shown and described with reference a hobbing machine generally of the type shown in United States Patent No. 2,307,428, issued January 5, 1943, except that, among other things, the shape of the machine is slightly different, for example, the hob head is carried by a member slidably supported in a cylindrical aperture in the vertical column or frame rather than being supported on horizontal ways, and the mechanism for moving the Work head vertically is of a diferent arrangement.

Generally speaking, the machine is of vertical construction and comprises a base A, a vertical column or gooseneck B supported upon the base A, a work head C vertically movable upon vertically spaced pairs of ways 10, 11 on the column B, and a tool or hob head D carried by a cylindrical member slidably supported in the column B and adjustable therein horizontally toward and from the work head. The work piece to be hobbed, which may be a gear blank, a shaft to be splined, or the like, is adapted to be rotatably supported by a work spindle 12, forming a part of the work head C, and a tail center 13 carried by a tail slide 14 supported for movement toward and from the work spindle upon ways 15, 16 on the work head. A hob arbor 17 is rotatably supported in the hob head D, and during operation of the machine is rotated in timed relation to the rotation of the Work spindle 12 by a cut motor CM located in the lower part of the column B and operatively connected to the arbor and spindle. The work piece is moved vertically past the hob during the cutting Operation to elfect the normal feeding operation, by vertical movement of the work head C,

which movement is synchronized with the rotation of the hob arbor. Simultaneously With the other movements and in synchronism therewith, the arbor is moved axially to advance the unused portions of the hob, which is indicated at H by broken lines in Fig. 4, into cutting relation with the work piece, which work piece is rotated in a direction such that the peripheral portion engaged at any instant by the hob moves in a direction opposite to that of the axial movement of the hob. Rapid traverse means, including a reversible rapid traverse motor TM, is provided to cause relatively rapid movement of the work head to carry the Work piece from a Work loading position to the cutting position and to return the work head to the loading position after the cutting operation has been performed.

The hob head D, see Fig. 4, is attached to an end wall of a cylindrical member 18, which member is supported in a horizontal cylindrical aperture in the column B. The member 18 is mounted for horizontal movement and suitable means, such as a key and keyway, not shown, is provided to prevent rotation of the member, and adjusting means, such as a screw device, not shown, is provided for accurately positioning the member 18 horizontally in the cylindrical aperture by rotation of a dial 19 on column B. The housing 20 of the head D is connected to the member 1S so that it can be angularly positioned relative to the latter, and for this purpose it includes a boss 23 extending in a circular opening in the end Wall of the member 18. The housing 20 is held to the member 18 by suitable bolts, not shown, the heads of which are disposed in a circular groove 24 in the end wall of member 20, which groove is T shape in cross section.

The angular position of the head D relative to the cylindrical member 18 may be adjusted by a worm gear 25 bolted to the neck 23 and engaged by a worm 26 journalled in member 20, which worm is rotatable bya member 27. By this arrangement, the hob axis may bev disposed at any desired angle relative work piece.

The hob arbor 17 is mounted in a spindle sleeve 28 which is journalled in a tubular opening in the housing 20 by suitable antifriction bearings. The end of the arbor extending from the housing 20 is journalled in a bearing assembly 29 which is slidingly mounted on ways 30. The hob H is attached to the arbor between a shoulder 31 and a washer 32 by a nut 33 threaded on the arbo-r and pressing on a bearing sleeve 34 of an antifriction bearing in the bearing head 29.

The upper portion of the arbor 17, as viewed in Fig. 4, is splined and a drive gear 35, which is bolted to the upper end of sleeve 28, is slidingly keyed into the splines so that the arbor may be rotated as it moves axially relat1ve to the drive gear. The upper end portion of the arbor has a bore therein, and a screw 36, which is bolted to a cap 37, depends into the bore. A nut 38 is bolted to the upper end of the arbor and threadingly receives the screw 36, whereby relative rotation between the arbor and the screw causes axial movement of the arbor relative to the screw. Any possible backlash between the threads of the screw and nut is obviated by a second nut 39 which to the axis of the is threaded on the screw and which may be rotated and drawn against nut '3'8 and locked from rotation relative to the latter by a sleeve 40 having longitudinally extending internal teeth engageable vin serrations on the exteriors of nuts 37, 3%. The cap 37 is rotatively supported on the hu-b of the vdrivin-g gear 35 for arbor 17 by a thru-st bearing structure 41, the cap being provided with 4a flange which is bolted to the outer race 42 of the Ibearing structure. The cap 37, and yconsequently the screw 36, may rotate relative to the arbor 17, but the cap or screvi cannot move axially.

'Ihe cap 37 is adapted to be rotated relative to the arbor to advance the latter on the screw by differential gearing driven by the drive 4'gear 35. The differential drive comprises a gear -44 mounted on the gear 35 and keyed thereto as at 45. The gear 44 is adapted to mesh with a gear 46 mounted on a bushing 47 journalled on a shaft 48 by anti-friction bearings. The gear 46 is keyed to a gear 49 which is also mounted on the bushing 47 and which meshes with a ring gear 50 mounted on the louter race member 42 of the bea-ring structure 41 and keyed thereto as at 51. The gears 46, 49 may be moved into andl out of engagement with gears 44, 50 by rotation of the shaft 48 so that the drive for the cap 37 may be selectively connected and disconnected. For this purpose the shaft 48 has the lower -end thereof journalled in -a bore 51, and the opposite end is journalled in a bearing 52 axially aligned with the bore. The portion of the shaft 48 on which the gears 46, 49 are journalled is eccentric to the axis of the bore and bearing, and the gears are moved into and out of engagement with gears 44, 50 by the eccentric movement of the shaft portion on which they are mounted. A crank handle 53 is provided for rotation of the shaft 48 and a detent structure 54 is provided for releasably retaining the shaft in the gear engaging and disengaging positions.

The gears 44 and 50 are of the same diameter, and gears 46 and 49 are ofthe same diameter, but the number of teeth on the gears of corresponding diameters vary slightly so that the gear 50, and hence cap 37 and screw 36, will lose one revolution for approximately every 10,000 revolutions of the arbor and cause the screw to advance the arbor approximately one screw thread for each 10,000 revolutions of the arbor. For example, the number of teeth on gears 44, 46, 49, and 50 may be 244, 8l, 83 and 250, respectively, to produce this speed reduction. If the screw 36 -has ten threads to the inch, the resultant axial movement imparted to the arbor 17 will be approximately one ten millionths of an inch per revolution of the arbor. The direction of axial movement of the arbor depends upon the ratios of the teeth on the gears 44, 46, 49 and 50 and the direction of pitch of the threads on the screw, and as brought out hereinbefore, the direction of movement of the arbor should be opposite to the direction of movement of the portion of the work piece tangentially engaged by the hob at any given instant.

After the arbor 17 has advanced to the extent desired i. e., until all of the available cutting portions of the hob has been use, it may be retracted onto the screw 36 for a succeeding period of operation with a new hob by rotating the cap 37 relative to the arbor. This is accomplished by disengaging gears 46, 49 from gears 44, 50, respectively, and turning the cap by a wrench engaging a polygonal head 55 on the screw 36, which head projects through an opening in the cap.

The arbor drive gear 35 is driven by the cut motor CM through a main drive shaft 56 journalled in the column B and which has a pulley 57 mounted thereon which is driven by the cut motor through a belt. The main drive shaft 55 is adapted to drive a parallel, splined shaft 58 which is journalled at one end in a bearing 59 located in the worm gear 25 and the opposite end is supported in a gear 60 journalled in a web 61 of a cylindrical boss structure 62 which projects from the rear wall of column B. The gear 60 is driven by a gear 63 mounted on the drive shaft 55, and gear 60 is splined to the shaft 58 s0 that the latter may be driven throughout the horizontal adjustments of the hob head. The forward end of the shaft 58 which extends into the hob head housing 20 has a helical gear 64 thereon which drives a helical gear 65 mounted to one end of a shaft 66 journalled in suitable antifriction bearings, and the opposite end of which hsaft 66 has a gear 67 which drives the arbor driving gear n win be seen that the heb arbor 17 is driven 8 attached to the lower end of the spindle.

by the cut motor and as the arbor rotates it is simultaneously and continuously moved axially. 'The hob head C may be positioned so that tli'e axis of arbor 17 may be at any desired angle relative tothe axis of the work spindle 12 and the hob may be adjusted to and from the axis of the work spindle 12, as desired.

The work spindle 12, which is 'tubular in construction, has its upper end journalled by suitable antifriction bearings in a cylindrical boss formation 70 on the work head C, and its lower end is journalled in an antifriction bearing in an opening through the bottom wall of the work head housing 71. Preferably, the work spindle 12 is provided with a pncumatically operated chuck for holding the work pieces. The Ichuck is not shown as such chucks are well known, however, a portion of the pneumatic mechanism 72 for operating the chuck is shown The spindle 12 is driven in synchronism with the hob arbor 17 by the -cut motor CM, through a drive mechanism which includes a vertical shaft '73 the upper end 'of which is journalled in the column B and is 'provided with a helical gear 74 driven by 'a helical gear 78 on shaft 56. The shaft 73 projects downwardly yinto ya channel 79 formed in the column B and is splined throughout a substantial portion of its length. The splined portion of the shaft 73 is slidably engaged by a helical gear 80 splined thereto. 'The gear 80 is journalled in a projection 81 integral with the housing 71 and which extends into the channel 79. A cross shaft '83 having one end journalled in the projection 81 and the opposite end journalled in a partition Wall 84 of the work head housing, is driven by gear through a gear 85 mounted on 'the endl of the shaft journalled in the projection; It will be seen that the drive between gears 80 and 85 will be maintained throughout the vertical range of movement -of the work head C by reason Vof the spline connection between shaft 73 and gear 80.

The shaft 83 drives a speed change rgear train, indicated generally at 87, which is located within the front compartment 88 formed in the Work head housing 71. The gear train 'drives a shaft 93, which comprises one input element of a differential Y94v in the drive for the work spindle 12. The output of the differential 94, comprises a shaft 96 having a worm 97 which drives a worm gear 98 integral with the spindle 12.

The differential 94 comprises a cage 100 carrying four planetary gears 101 which gears mesh with vtwo axially aligned sun gears 102, 1'0'3 formed on the adjoining ends of the aligned input and output shaft 93, 96, respectively. The cage has a helical gear y104 by which rotation of the cagel is controlled. When the cage is stationary and shaft 93 rotates, 'shaft 96 will be driven directly. If the cage is rotated, the shaft 96 is driven at a speed which is the algebraic sum of the speeds of the cage and input shaft 93. When it is desirable to cut spur teeth on gear blanks, for example, the cage is locked to prevent rotation thereof and the work piece will be moved past the hob to effect the cutting of straight gear teeth. In the event it is desired to cut spiral teeeh, the cage is rotated 'to change the speed of rotation of the work spindle 12 relative to the movement of the work head C and cause spiral teeth to be formed, as is well understood by those familiar with the art.

The work head C, see Figs 5' and 6, is vsupported by a screw 107, the lower yend of which is non-rotatively attached to the base A and the .upper end of which has a tubular nut A108 threaded thereon. Preferably, the screw shaft 107 is enclosed in a telescoping guard 109, for shielding the screw from chips and other foreign particles which might otherwise collect on the threads thereof. The nut 108 is journalled at vits lower end in an antifriction combination thrust bearing 110 mounted in the lower walls of the work head housing and its upper end is journalled in bearings 111 mounted in a bracket 112 integral with `the partition 84 in the work head housing 71. When the nut 108 is rotated, by means described hereinafter, the head C is `moved vertically in a direction depending on the direction of rotation of the nut. The screw 107 extendsthrough a flanged ring 113 which is mounted in an opening in the lower wall of the work head housing and bearing 110 is secured in the ring. The inner race of the 'bearing 110 is attached to the nut 10S.

The nut 108 is adapted to be rotated by either the cut motor CM yor the traverse lmotor TM, and automatically controlled means is provided for rendering one or the other of the motors effective to drive Vthe nutat the' proper times and in the proper direction.w The cut motor drive mechanism for the nut 108 includes a worm gear 115 in mesh with and driven by, a worm 116 formed on a shaft 114 rotatably supported in the work head housing 71 and operatively connected to the shaft 93 by a speed change gear train 118, see Fig. 6. The worm gear 115 is rotatively mounted on the nut 108 and is provided with a downwardly extending hub 117, the lower portion of which is externally splined. A clutch collar 120 surrounds the hub 117 and has teeth slidingly engaged with the hub splines for connecting the work gear 115 with the collar 120 throughout a range of sliding movement of the collar on the hub. A sleeve 121 keyed to the nut 108 immediately below the lower splined end of the hub 117 of the worm gear 115, has its upper portion splined as at 122 to receive the internal teeth of the collar 120 when the collar is lowered over the upper portion of the sleeve. Thus, by sliding the clutch collar 120 downwardly and upwardly, as viewed in Fig. 7, the worm 115 is drivingly connected and disconnected, respectively, with the nut 108.

The clutch collar 120 is moved vertically by a yoke 123 which has pins 124 extending into aperipheral groove 125 formed in the collar. The yoke is moved by an electrical solenoid 126 which has an armature 127 associated therewith and which is connected with a rack member 128 which cooperates with pinion 129 formed on a rocker shaft 130 to rotate the latter shaft when the armature is attracted and released from the solenoid. An arm 132 on the rocker shaft is connected to the clutch yoke 123,

and when the solenoid is energized, the yoke is lowered,

as viewed in Fig. 7, for connecting gear 115 with the nut 108. When the solenoid is deenergized, the 1armature drops and the yoke is raised to disconnect the gear 115 and nut 108. The solenoid 126 is controlled by a suitable control circuit, not shown, according' to the vertical position of the Work head C relative to the hob head.

The traverse motor TM is mounted on the exterior of the left hand wall of housing 71, as viewed in Fig. 7, and it is drivingly connected with the nut 108 by a shaft 133 connected to the motor armature shaft and journalled in a bearing housing 134. A helical gear 135 connected to the end of shaft 133 opposite the motor, is continuously in mesh with a helical gear 136 formed integral with the nut 108. The traverse motor is connected in driving relation with the nut 108 at all times, and it is adapted to rotate the nut at a rapid rate, relative to that at which the nut is driven by the cut motor, for moving the work head C vertically to cutting position and to return the work head to loading position. The control system for the hobbing machine is arranged such that when the nut 108 is driven by gear 115, the traverse motor is deenergized and it may be driven through the gears 135, 136.

When the hobbing machine is used to cut spiral gear teeth, or the like, the cage 100 of the dilerential 94 is driven in timed relation to the rotation of the nut 108, as shown, the cage 100 is operatively connected to the nut 108 by drive mechanism which includes miter gears 140, 141 on the upper end of the nut 108 and a horizontally extending shaft 142, respectively, seen in Fig. 7. The shaft 142 is adapted to drive a speed change gear train 143 located in a compartment formed in the side of the work head housing 71 and opposite the rapid traverse motor. The gear train 143 drives a' shaft 144 having a helical gear 145 thereon which drives the gear 104 connected to the cage 100. The rotation of the cage 100 imposes a differential in speed between theinput shaft 93 and the drive shaft 96 for the spindle 12 according to the speed of the nut 108. If it is desired to cut straight gear teeth, or the like, the gear train 143 is disconnected and the cage 100 held against rotation with the result that a direct drive is had through the differential.

It will be seen that as the work piece is fed vertically past the hob, the piece is rotated on its axis at a certain speed relative to the speed of the hob, and the rate of vertical feed of the work piece has a denite relationship to the hob speed. The hob will also be continuously fed axially during the cutting operation and the rate of axial movement of the hob preferably is such that it will require a number of hours to use all of the available cutting portions thereof. It is desirable to have an automatic indicating mechanism for signalling the termination of the hob movement, and for this purpose, a limit switch 150, which may be seen in Fig. 4, is provided in 6 a recess in the hob head housing 20. vThis switch s'connected in asignal circuit, notshown, such as alight and/or bell circuit, so that when the switch is closed the signal circuit will be energized. The switch is movable to its closed position by a crank lever 151 pivoted at 152 in an opening through a wall of the hob head structure, and one end of the lever is positioned adjacent the side of cap 37. The lever 151 is adapted to be moved counterclockwise, as viewed in Fig. 4, by upward movement of a ring 154 attached to a sleeve 155, positioned within cap 37, by a plurality of spacers 157 and bolts 158, one each of which are shown in the drawings. It will be understood that the cap 37 has appropriate openings forY receiving the spacers and bolts. The ring 154 is adapted to be moved upwardly by three ngers159, only one of which appears in the drawings, which fingers are pivoted in'slots in the sides of the cap 37 and' spaced equally thereabout. The outer ends of the fingers 159 are adapted to engage the underside of the ring and the inner ends of the lingers are adapted to be engaged by 4a ring 160 threaded on the exterior of the sleeve 40 as the end portion of the arbor 17 travels toward the lower end of the cap 37. The ngers 159 are adapted to be tilted by the travel of ring 160 to raise the ring 154 for rotating switch arm 151 to close the signal circuit. This condition is illustrated in Fig. 4, wherein the position of the ring 160 at the end of the axial movement of the hob is shown in dotted lines. The point of travel of the arbor 17 at which the switch is operated may be adjusted by varying the position of the ring on the sleeve 40, as is indicated in dotted lines in Fig. 4. The ring 160 may be locked in the proper position by a lock nut 162. When the screw 36 isv rotated to draw the arbor 17 into the cap 37, as when the new hob is to be placed in operation, the ring 160 is removed from fingers 159. A coil spring 163 is interposed between the end wall of the cap 37 and the outer end of the sleeve 155 to urge the sleeve toward the base of the cap to release the switch lever 151 when the rljor 17 is initially positioned for operation with a new In operation of the machine, a new or sharp hob is mounted on the arbor 17 and the latter is drawn upwardly on the screw 36, as viewed in Fig. 4, so that the end of the hob will initially engage a work piece mounted in the spindle 12. The work piece is chucked in the spindle 12 and secured therein by the tail stock member 13 and the hob head' D is adjusted horizontally so that when it engages. the work piece it will cut to the proper depth. It is to be understood, of course, that the hob head D will be rotated or positioned approximately 90 from the position shown in Figs. l and 2 so that the axis of the hob will extend transverse with respect to the axis of the work piece. Forpurpose of explanation, it will be assumed that the machine is set for conventional hobbing and that the work pieces are loaded when the work head is in its lowest position. The automatic control of the cut motor, the rapid traverse motor and the solenoid 126 may be effected by a control system, parts of which are shown at and 166, and which may be similar to that described in the aforementioned patent and in which case the solenoid 126 would be connected in the control circuit in such a manner that it would be energized and deenergized simultaneously with the energization and deenergization of the rapid traverse motor. The cycle of operation is initiated by actuation of the start push button switch 165 which causes the traverse motor to rapidly elevate the work head C to a point at which the work piece closely approaches the hob. The traverse motor is then automatically deenergized and the clutch solenoid 126 is energized to connect gear 115 with the nut 108 so that the work head C will continue to move vertically but at a relatively slow rate past the hob H while the hob and work piece both rotate in timed relation. After the work piece is moved past the hob, the clutch solenoid and the cut motor are automatically deenergized and the nished work is removed from the spindle 12, after which the start push button switch 165 is again depressed thereby causing the traverse motor to operate in a reverse direction from its initial direction to rapidly lower the work head C to the loading position, at which point the traverse motor is automatically deenergized. A new work piece is mounted to the work head and the cycle of operation is repeated as described.

During the cutting operation thehob H is continuously advanced in the direction which is counter to the the periphery off the work piece at 1ts point ofengagement with the hob so that unusedl portions of the hobwill be continuously fed; into tangential engagement with the Work piecesv and the initial engagement of the unused` portions with the work pieces will be with portionsof the work which have been cut by used portions of the hob. In other words, the used portions of the hob will rough out the cuts and the less used portions will perform the nished cuts so that greater accuracy is achieved in the finished work piece and at the same time a maximum useful life of the'hob is attained.

The relative movements of the hob and work piece in one example ofl carrying out the method of the. invention is illustrated in Fig.. 9. In this particular instance, the work piece W, whichL isa gear blank, is rotated clockwise in. cutting, relation with the hob and it is moved upwardly on its axis for feeding to the hob. The hob is rotated fork conventional hobbing and at the same time it is slowly advanced axially in a direction counter to that of. the portion of the periphery of the work piece engaged thereby. The rate of axial advance of the hob is relatively slow and this movement does not enter` into the feed considerations. Throughout a considerable number of cycles of hobbing operations, however, the hob will be advanced from one end to the other of its effective cutting portions. As explained hereinbefore, this movement continually and gradually present'sV a new portion of the hob into cutting engagement with portions of the work previously cut by used portions of the hob. It may,l in some cases, be desirable to move the hob vertically and parallel to the axis ofthe work piece to effect axial feeding, rather than move the work piece, and such arrangement falls within the contemplation of the invention.

It will be apparent by those familiar with the art that thel directions of movement of the hob and the work piece may be reversed and the relative speeds thereof may be altered, if desired, by appropriate substitution of or by the addition of gears in either of the gear trains 87, 91 or 143, and for this purpose it may be desirable to provide interchangeable gear structures, Regardless of the change in direction of rotation of the hob and the work piece, it is essential to the present method that the direction of axial movement of the hob with respect to the direction of rotation of the work piece be retained which causes the direction of advance of the hob to be in the opposite direction to the movement ofthe peripheral polsition of the work piece tangentially engaged by the ho It. should be noted that the screw 107 on which the work head C is moved vertically is located on an axis which is substantially at the center of mass of the work head C so that a minimum of stress is applied to the E direction of movement of guides 10, 11, 15 and 16, which increases the accuracy f' and durability of the machine. This arrangement also permits the Work spindle 12 to be located adjacent to the column B which provides a minimum of overhang of the work head and provides greater stability for the spindle. In addition, the structural arrangement shown provides a relatively compact driving mechanism for rotating the work spindle 12, the hob arbor 17 and the elevating nut 108.

Suitable means may be provided for lubricating the various gears and bearings and a suitable coolant may be 8 fed= to thev hobi and; work pieces, but since such means are' commonly used, they have not been shown in the embodiment of the invention described;

While the preferred form of the invention has been de.- scribed infconsiderable detail, it is to be understood that thisisby way of example only and that the invention is not limited to the particular details shown and described.

Having thus described our invention, we claim:

1. The method of hobbing which comprises, rotating a hob in cutting relation with a work piece rotated in timed relation therewith, producing relative movement therebetween longitudinally ofthe axis of rotation of the work piece to produce a feeding movement between the hob and work piece, and simultaneously and continuously slowly moving said hob axially in a direction opposite to the direction of movement of the portion of the periphery of the work piece engaged by the hob at any given time to graduallyy advance the hob relative to the work piece and thereby bring successive portions of the hob into cutting position.

2. The method of hobbing which comprises, successively rotating work pieces in cutting relation with a rotating hob, producing relative movement between the work pieces and hob longitudinally of the axis ofv rotation of the workpieces to produce a feeding movement between the hob and the work pieces being cut, and simultaneously and continuously slowly moving said hob axially in a direction opposite to the direction of movement of the portion of the periphery of the work piece engaged by the hob at any given time to gradually advance the hob relative to the workpiece and thereby bringl successive portions of the hob into cutting relation with successive workpieces.

3, The method of hobbing a number of workpieces whichA comprises bringing successive workpieces rotated about a common axis in a given direction into hobbing engagement with a rotating hob having an appreciable longitudinal cutting surface, producing relative movement therebetween longitudinally of the axis of rotation of the workpieces to produce a feeding movement between the hob and workpieces, and producing a continuous slow unidirectional relative movement between the workpieces and hob axially of the hob during hobbing of the workpieces and' in a direction opposite to the direction of movement of the portions of the workpieces engaged by the hob whereby the segment of the hob engaging the workpieces is gradually moved lengthwise of the hob during cutting of the workpieces and causing roughing, cuts in the workpieces to be made by used portions of the hob and finishing cuts therein to be made by continually advanced unused portions of the hob.

References Cited in the tile of this patent UNITED STATES PATENTS 611,277 Reinecker Sept. 27, 1898 2,122,219 Staples June 28, 1938 2,211,611 Staples Aug. 13, 1940 2,231,866 Adams Feb. 18, 1941 2,273,050 Kruse Feb. 17, 1942 2,481,974- Bradner Sept. 13, 1949 2,483,810 Cotta Oct. 4, 1949 2,484,856 Purvin Oct. 18, 1949 2,516,750 Brower July 25, 1950 2,537,967 Carlin Jan. 16, 1951 

